In the microwave monolithic integrated circuit using a compound semiconductor substrate, conventionally, on the same compound semiconductor substrate such as GaAs, an active element such as a field effect transistor (hereinafter, abbreviated as an FET) and an MIM capacitor as a passive element are formed. (Refer to FIG. 1, Japanese Patent Application 2002-184946).
In conventional processes for manufacturing such an MMIC, the active element and passive element are manufactured by different manufacturing processes. For example, in the processes for manufacturing FET as an active element, a source electrode and a drain electrode composed of an ohmic metal AuGe/Au respectively are formed and a gate electrode composed of a Schottky metal Ti/Pt/Au is formed between these electrodes in an active area on a GaAs substrate.
On the other hand, in the MIM capacitor, a lower electrode composed of a Al or Ti/Al metal film is formed on the GaAs substrate and a dielectric layer composed of an SiN film, for example, is formed on the lower electrode. The SiN film is formed also on a surface of the FET. Then, an upper electrode composed of Ti/Pt/Au, for example, is formed on the SiN film. Upper electrodes are formed also on the surfaces of the source, drain and gate electrodes of the FET via contact holes formed in the SiN film. Thus the MMIC is completed.
However, in the MMIC having such structure as mentioned above, the step for forming the lower electrode of the MIM capacitor is carried out as a separate step from the step for forming the FET elements. Thus, the whole manufacturing steps become longer, resulting in low throughput. The reason why the manufacturing steps of the two must be different from each other is that the lower electrode of the MIM capacitor and the electrodes of the FET must be formed by different metallic materials. Therefore, a semiconductor device is desired, which realizes short manufacturing steps and enhances reliability of active and passive element portions.
One of the objects of the present invention is to provide an element structure of the MMIC having the active element and MIM capacitor enabling a reduction in the number of the manufacturing steps of the MMIC and also to provide a manufacturing method therefor.